Rajat, can you please explain the problem in more detail and let us know your system specs (especially your motherboard). Do you get any error codes or warnings that could assist us?
my mother board is intel centrino. actually the problem i think is with some hardware drivers. I think it because the problem started after i put a pen drive into my laptop.
thanks for replying.
This Pendrive / Flashdrive can you scan it with an Anti Virus application and a Spyware application ? (if you don't have these please see links below), also can you remove the Pendrive (using Safely Remove Hardware) and scan your Computer for Virus and Spyware.